//! Log rotation helper

use std::fs::{rename, File};
use std::io::Read;
use std::os::unix::io::{FromRawFd, IntoRawFd};
use std::path::{Path, PathBuf};

use anyhow::{bail, Error};
use nix::unistd;

use crate::fs::{make_tmp_file, CreateOptions};

/// Used for rotating log files and iterating over them
pub struct LogRotate {
    base_path: PathBuf,
    compress: bool,
    max_files: Option<usize>,
    /// User logs should be reowned to.
    options: CreateOptions,
}

impl LogRotate {
    /// Creates a new instance if the path given is a valid file name (iow. does not end with ..)
    /// 'compress' decides if compresses files will be created on rotation, and if it will search
    /// '.zst' files when iterating
    ///
    /// 'options' is used for newly created compressed files.
    pub fn new<P: AsRef<Path>>(
        path: P,
        compress: bool,
        max_files: Option<usize>,
        options: Option<CreateOptions>,
    ) -> Result<Self, Error> {
        if path.as_ref().file_name().is_none() {
            bail!("logrotate path does not contain a file name");
        }
        Ok(Self {
            base_path: path.as_ref().to_path_buf(),
            options: options.unwrap_or_default(),
            compress,
            max_files,
        })
    }

    /// Returns an iterator over the logrotated file names that exist
    pub fn file_names(&self) -> LogRotateFileNames {
        LogRotateFileNames {
            base_path: self.base_path.clone(),
            count: 0,
            compress: self.compress,
        }
    }

    /// Returns an iterator over the logrotated file handles
    pub fn files(&self) -> LogRotateFiles {
        LogRotateFiles {
            file_names: self.file_names(),
        }
    }

    fn compress(
        source_path: &Path,
        target_path: &Path,
        options: &CreateOptions,
    ) -> Result<(), Error> {
        let mut source = File::open(source_path)?;
        let (fd, tmp_path) = make_tmp_file(target_path, options.clone())?;
        let target = unsafe { File::from_raw_fd(fd.into_raw_fd()) };
        let mut encoder = match zstd::stream::write::Encoder::new(target, 0) {
            Ok(encoder) => encoder,
            Err(err) => {
                let _ = unistd::unlink(&tmp_path);
                bail!("creating zstd encoder failed - {}", err);
            }
        };

        if let Err(err) = std::io::copy(&mut source, &mut encoder) {
            let _ = unistd::unlink(&tmp_path);
            bail!("zstd encoding failed for file {:?} - {}", target_path, err);
        }

        if let Err(err) = encoder.finish() {
            let _ = unistd::unlink(&tmp_path);
            bail!("zstd finish failed for file {:?} - {}", target_path, err);
        }

        if let Err(err) = rename(&tmp_path, target_path) {
            let _ = unistd::unlink(&tmp_path);
            bail!("rename failed for file {:?} - {}", target_path, err);
        }

        if let Err(err) = unistd::unlink(source_path) {
            bail!("unlink failed for file {:?} - {}", source_path, err);
        }

        Ok(())
    }

    /// Rotates the files
    /// if the 'compress' option was given it will compress the newest file
    ///
    /// e.g. rotates
    /// foo.2.zst => foo.3.zst
    /// foo.1     => foo.2.zst
    /// foo       => foo.1
    pub fn do_rotate(&mut self) -> Result<(), Error> {
        let mut filenames: Vec<PathBuf> = self.file_names().collect();
        if filenames.is_empty() {
            return Ok(()); // no file means nothing to rotate
        }
        let count = filenames.len() + 1;

        let mut next_filename = self.base_path.clone().canonicalize()?.into_os_string();
        next_filename.push(format!(".{}", filenames.len()));
        if self.compress && count > 2 {
            next_filename.push(".zst");
        }

        filenames.push(PathBuf::from(next_filename));

        for i in (0..count - 1).rev() {
            if self.compress
                && filenames[i].extension() != Some(std::ffi::OsStr::new("zst"))
                && filenames[i + 1].extension() == Some(std::ffi::OsStr::new("zst"))
            {
                Self::compress(&filenames[i], &filenames[i + 1], &self.options)?;
            } else {
                rename(&filenames[i], &filenames[i + 1])?;
            }
        }

        if let Some(max_files) = self.max_files {
            for file in filenames.iter().skip(max_files) {
                if let Err(err) = unistd::unlink(file) {
                    eprintln!("could not remove {:?}: {}", &file, err);
                }
            }
        }

        Ok(())
    }

    /// Conditional rotate if file bigger than 'max_size'
    pub fn rotate(&mut self, max_size: u64) -> Result<bool, Error> {
        let metadata = match self.base_path.metadata() {
            Ok(metadata) => metadata,
            Err(err) if err.kind() == std::io::ErrorKind::NotFound => return Ok(false),
            Err(err) => bail!("unable to open {:?} - {}", self.base_path, err),
        };

        if metadata.len() > max_size {
            self.do_rotate()?;
            Ok(true)
        } else {
            Ok(false)
        }
    }
}

/// Iterator over logrotated file names
pub struct LogRotateFileNames {
    base_path: PathBuf,
    count: usize,
    compress: bool,
}

impl Iterator for LogRotateFileNames {
    type Item = PathBuf;

    fn next(&mut self) -> Option<Self::Item> {
        if self.count > 0 {
            let mut path: std::ffi::OsString = self.base_path.clone().into();

            path.push(format!(".{}", self.count));
            self.count += 1;

            if Path::new(&path).is_file() {
                Some(path.into())
            } else if self.compress {
                path.push(".zst");
                if Path::new(&path).is_file() {
                    Some(path.into())
                } else {
                    None
                }
            } else {
                None
            }
        } else if self.base_path.is_file() {
            self.count += 1;
            Some(self.base_path.to_path_buf())
        } else {
            None
        }
    }
}

/// Iterator over logrotated files by returning a boxed reader
pub struct LogRotateFiles {
    file_names: LogRotateFileNames,
}

impl Iterator for LogRotateFiles {
    type Item = Box<dyn Read + Send>;

    fn next(&mut self) -> Option<Self::Item> {
        let filename = self.file_names.next()?;
        let file = File::open(&filename).ok()?;

        if filename.extension() == Some(std::ffi::OsStr::new("zst")) {
            let encoder = zstd::stream::read::Decoder::new(file).ok()?;
            return Some(Box::new(encoder));
        }

        Some(Box::new(file))
    }
}